Hey all, new guy from Sydney, Australia.
Ive been reading a hell of a lot about ebikes/batteries over the last 6-8 months and have begun my first project. A 48v 1500w brushless motor and matching controller, and I'm planning on making a 13S8P li-ion battery with BMS, with the cells coming from some 12 cell laptop batteries. I have already bought 1 battery from the seller and tested the cells, they seem to all be 2400 - 2600mAh and charge/discharge quite well (testing on a balance charger from Jaycar).
Now i am a bit of a noob when it comes to hands on electronics (this being my first project), but don't get me wrong, I've watched countless videos and read article after article about Li-Ion, LiFePO4, LiCo etc. and understand that Li-ions are the most dangerous when not treated or monitored right (hence the BMS), but I am just after a second opinion.
Anyway, I am just running this by everyone to get their thoughts and to see if I'm on the right track:
With the 3.7v 2600mAh cells in 13S8P, that would give me a 48.1v 20.8Ah pack. With the 48v motor drawing MAX 40A, is this a well suited battery idea? As i understand you shouldn't draw more than 2C otherwise you get too high of a voltage sag/heat buildup etc. I will also buy a 40A peak / 20A continuous balancing BMS and wire that into the pack <- my insurance policy
Now when the batteries are at full charge of 4.1-4.2v, is the total 54.6v too high for the motor? or will it simply 'use what it needs'?
Secondly, am i right in thinking that if i charge each cell to 4.1v rather than 4.2v, and discharge to say 3.2v rather than 3.0v, will that increase the lifetime of the batteries (number of cycles)?
Finally, with so many cells coming in a 1S4P configuration, what are people's thoughts on using some coin magnets to temporarily connect these cells in series to balance charge? I have heard people say its a HUGE no no, but then others say its ok. Personally I don't understand how it will affect the charging such that the magnetic field is not changing, and with my understanding, shouldn't cause an issue.
Thanks all, and I am having such a great time tinkering away on all this stuff. Its nice to finally take my mind off uni studies to find a hobby which is also practical by saving me more money in the long run
